Thursday, Feb 20, 2014 - 8:00 PMTonight on Nightly Business Report, Wal-Mart, the world's largest retailer, says it won't earn as much money this year as many had hoped. What's holding Wal-Mart back? And, Facebook pays a whopping $ 16b for WhatsApp, a company few have heard of before today. How does it make money and who are the guys behind it?. D